South Korea on Thursday started enforcing a new law aimed at curbing the country's notorious cyber bullying by preventing Internet users from hiding behind false IDs.

Under the "Internet real-name system," the country's major portals and news media websites will be compelled to record the real IDs of users when they post entries.

Portal operators will be obliged to disclose personal information such as names and addresses of cyber attackers when their victims want to sue them for libel or infringement upon privacy.

"From today, users will be asked to give their real name and social security number before being allowed to write their postings," said a spokesman of Daum, one of the country's top portals which boasts of 38 million users.

Cyber bullying has become a social issue in South Korea as many celebrities often fall victim to abuse and malicious attacks.

Many Internet users, taking advantage of anonymity, have made a hobby of writing malicious messages on websites, accusing celebrities of sex scandals or having plastic surgery, experts said.